Water waves breaking on a beach, not only suspend beach materials, but also produce a longshore current. The longshore current carrying the suspended beach material is called the littoral drift. Noticeably, a longshore current can also be generated by winds or other natural forces. Traditionally, referring to the predominant littoral drift direction, coastal engineers and scientists term the beach benefiting from accretion, as the upstream beach of the inlet, and the beach suffering from erosion, as the downstream beach.
In the past, beach erosion in the downstream beach of an inlet has been considered by those in the coastal engineering field to be a problem without a solution. Also within the inlet area, sedimentation in the navigation channel also accompanies beach erosion in the downstream beach, compounding the problem. The beach/inlet problems result from: (1) the inlet interrupts of the littoral drift, and traps the sediment in the navigational channel of the inlet during flood tides and storms, so that the downstream beach starves for the sediment, and (2) diffraction of the obliquely incident waves by the jetties of the inlet, and refraction by the nearshore topography, cause the uneven wave set-up on the downstream beach, inducing a nearshore circulation cell carrying beach materials to form offshore bars, and/or to shoal the navigation channel of the inlet. Here, the wave set-up is interpreted as the mean water surface displacement, produced by the wave excess momentum (called the radiation stress) of the breaking waves inside the surf zone. The mean water displacement increases linearly with water depth as the shore is approached. This water surface slope provides a hydrostatic pressure gradient for the driving force of the nearshore circulation cell. The reference regarding this phenomenon is explained in the paper "A Numerical Model of Nearshore Currents Based on a Finite Amplitude Wave Theory" by M. Yamaguchi in the Proceedings of the 21st International Conference on Coastal Engineering, Chapter 64, Pages 849-863, 1984.
Since the problems aforesaid of coastal hydrodynamics of the beach/inlet system is coupled, both problems, (a) the problem of beach erosion, and (b) the problem of inlet sedimentation, must be solved simultaneously. This invention provides a method and device for bypassing the littoral drift and for stabilizing the downstream beach.